1. Field of the Invention
The present invention relates generally to visual displays, and more particularly to liquid crystal displays with increased contrast and gain between the energized liquid crystals and the background by directing more light incident on the display toward the viewer in a specific and controllable manner.
2. Description of the Related Art
Passive liquid crystal display viewing screens are utilized in hundreds of applications for displaying data to one or more viewers. Such displays are commonly found on wrist watches, clocks, gas pump displays, modern telephones, automobile clocks and instrument clusters, and other applications. These displays typically include a generally light colored background which is visible behind the liquid phase of a liquid crystal composition. When the liquid crystal is energized to display a particular set of information, the liquid crystal turns much darker and creates a contrast between the background and the displayed information. However, under some lighting conditions the contrast is difficult or nearly impossible to see when the conditions minimize the contrast because of reflection on the top layer of the display, low light conditions, high ambient light or other such reasons such as a limited view area.
U.S. Pat. No. 5,534,386 issued to Peterson et al. and entitled xe2x80x9cHomogenizer Formed Using Coherent Light and A Holographic Diffuserxe2x80x9d discloses a homogenizer in a sheet and a method of making the homogenizer. The homogenizer includes a micro-sculpted surface structure replicated in the sheet which homogenizes the light, and controls the direction and shape of its distribution. This patent discloses that the homogenizer may be used in a transmissive application as well as a reflective application. In the transmissive application the homogenizer is placed between a light source and a viewing area whereby the light passing through the homogenizer improves the quality of light according to the micro-sculpted surface structure. In the reflective application, the homogenizer includes a reflective layer deposited on the same surface as the micro-sculpted surface structures and wherein the reflective layer conforms to the surface structure. Light is then projected onto the homogenizer and reflected by a reflective surface of the homogenizer reflective layer. The reflective surface faces outward in such a construction.
One problem with this construction is that the flow characteristics of the reflective material deposited on these microstructures results in a loss of definition of the structures. For example, a 5xc2x0 light shaping diffusing surface (i.e., one that produces a cone of light having an angular distribution of 5xc2x0) formed in the homogenizer material results in a 20xc2x0 effective angle on the outward facing reflective surface after deposition of the reflective layer on the embossable layer. Another problem with such a surface is that the reflective layer is somewhat dark and results in a grainy image having medium to low resolution quality. An additional problem with such a surface is that it cannot be cleaned with any frequency because the reflective surface of the layer will be damaged or partially removed when cleaned. Cleaning is not an essential requirement for a liquid crystal display structure incorporating the homogenizer. However, the fact that the surface is too metallic results in excess glare as well as too grainy of an image. A loss of definition of the microstructure is an important problem which will significantly decrease the quality of a liquid crystal display utilizing such a homogenizer.
U.S. Pat. No. 5,609,939 issued to Peterson et al. and assigned to the assignee of the present invention discloses a viewing screen either in a reflective mode or a transmissive mode which utilizes the homogenizer of the ""386 patent. The same problems described for the ""386 patent are also present in the ""939 patent. Related U.S. patents include U.S. Pat. No. 5,631,754 entitled xe2x80x9cHolographic High Contrast Viewing Screen Embedded in a Liquid Crystal Display,xe2x80x9d and U.S. Pat. No. 5,735,988 entitled xe2x80x9cMethod of Making Liquid Crystal Display.xe2x80x9d Related U.S. patent applications include Ser. No. 08/782,962 entitled xe2x80x9cApparatus for LCD Backlighting,xe2x80x9d Ser. No. 08/800,872 entitled xe2x80x9cMethod of Making Replicas and Compositions for Use Therewith,xe2x80x9d Ser. No. 09/052,586 entitled xe2x80x9cMethod of Making Replicas While Preserving Masterxe2x80x9d and xe2x80x9cMethod of Making Hard Substrate Diffuser,xe2x80x9d filed Aug. 24, 1998. These above patents and pending applications are incorporated herein by reference.
The present invention is directed to a liquid crystal display having improved viewing characteristics as a result of an improved light shaping diffuser or homogenizer construction incorporated into the display. One object of the present invention is to provide a liquid crystal display which is particularly well suited for use in passive light or poor lighting conditions. An additional object of the present invention is to provide a liquid crystal display which produces a background which is essentially of a white appearance or very light appearance. A further object of the present invention is to provide a liquid crystal display incorporating a homogenizer or diffuser producing a projected image having a satisfactory fine grain. An additional object of the present invention is to provide a liquid crystal display which directs a substantial portion of light incident the display toward a predefined viewing area in a particular shape or distribution. A further object of the present invention is to provide a viewing screen of the reflective type which homogenizes light and controls the direction and shape of distribution of light and which can be easily cleaned without damaging the homogenizer microstructure of the viewing screen. Another object of the present invention is to provide a reflective viewing screen wherein the definition or resolution of a light shaping surface microstructures of the viewing screen is maintained after adding a reflective layer. A still further object of the present invention is to provide a reflective viewing screen including a homogenizer that reduces the metalic appearance of the screen.
To accomplish these and other objects of the present invention, a liquid crystal display has a liquid crystal element with a front viewing surface and a rear surface. The liquid crystal display also has a substrate layer with a front side disposed against the rear surface of the liquid crystal element. The substrate layer also has a back side opposite the front side. A light shaping surface microstructure is carried in the front side of the substrate layer wherein the microstructure controls the directionality in which light propagates and scatters the light into a controlled distribution having the desired shape and smooth brightness variation. A reflective layer is deposited on the back side of the substrate layer and is capable of reflecting light back toward the front viewing surface of the liquid crystal element.
The reflective layer can be a metal layer of material vacuum formed or otherwise deposited on the back side of the substrate layer or can be some other layer of material having desirable light reflecting properties. The reflective layer is capable of reflecting light incident on the liquid crystal display thru the liquid crystal element.
In another embodiment, the microstructure is integral in the back side of the substrate layer and the reflected layer deposited over the microstructure.
A reference horizontal plane and a reference vertical plane are defined relative to the front viewing surface extending generally perpendicular relative to the screen. The viewing surface also has a reference normal axis perpendicular to the front viewing surface where the horizontal and vertical planes intersect. These imaginary planes define a field of view which has a viewing width angle measurable along the horizontal plane and a viewing height angle measurable along the vertical plane. Each viewing angle is determined by the shape and size of the micro-sculpted surface structure as well as the type of liquid crystal material utilized in the element.
Both the horizontal viewing angle and the vertical viewing angle have a central axis which is coaxial with the normal axis of the viewing surface thereby making the viewing area symmetrical relative to the viewing surface. In other embodiments, one or both of the horizontal and vertical reference planes may be rotated or offset from a vertical and horizontal reference axis of the viewing surface in order to project light toward a particular desired target wherein the field of view is rotated relative to the reference vertical and horizontal axis of the screen.
The field of view can be defined by both the vertical viewing angle and horizontal viewing angle and has a substantially constant output intensity of light created by the microstructure. This field of view may have a distribution or shape which is generally rectangular, circular, elliptical or such shape as desired for a particular liquid crystal display application.
The liquid crystal display of the invention is particularly well suited for passive or ambient light applications because it directs substantially all of the light photons incident the liquid crystal display to within a particularly defined field of view which can be very accurately controlled. Therefore, the reflective layer substantially increases the brightness of the display and makes it much easier to read information or data on the display.
In another embodiment of the invention, a front projection viewing screen is provided and has a substrate layer with a front viewing surface facing a viewing area and a back side opposite the front viewing surface. A light shaping micro-sculpted surface structure or microstructure is formed in the front viewing surface of the substrate layer which controls directionality of light propagating from the front viewing surface and scatters the light into a controlled distribution having a smooth brightness variation. A reflective layer is deposited on the back side of the substrate layer and is capable of reflecting light back toward the front viewing surface of the viewing screen.
In another embodiment, the microstructure is formed in the back side of the substrate layer. The reflective layer is deposited on the microstructure on the back side of the substrate layer. The viewing surface in this embodiment is a smooth front side of the layer.
The same characteristics apply for the projection viewing screen except that the liquid crystal display described above is not utilized. Instead, the viewing screen is used as a reflective viewing screen wherein an image is projected onto the screen. By placing the reflective layer on the back side of the substrate layer opposite of the microstructure or on the microstructure on the back side of the substrate layer, the problems with the viewing screen previously invented and patented by the assignee of the present invention are overcome.
In one embodiment, the viewing screen also includes an optional magnetic backing attached to the reflective layer on the back side of the substrate layer. The magnetic backing permits mounting the viewing screen to a metallic surface therefore rendering the viewing screen movable, removable, replaceable and portable as needed.
These and other objects, features and advantages will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention and without departing from the spirit thereof, and the invention includes all such modifications.